Everyone wants to hit the ball over the fence. It's the easiest way to score; you don't even have to be fast if you can smash the ball out of the park. If you watch major league baseball, the most amazing hitters are able to slap the ball out of the park with arm strength alone; however, the consistent, natural hitters are unlikely to use this method.
For smooth, consistent hitting there are several things you need to consider: first, and maybe the most important, your stance. You have to be comfortable in the batter's box. Try standing in the box in an athletic stance, without a bat. Your balance should be on your back foot, because this where a large portion of power comes from that is needed to crush the ball. As with all athletic stances, your feet should be width apart, with knees slightly bent and your weight should be on the balls of your feet.
Second on the list is your grip on the bat. The most common advice is to line your knuckles (the biggest knuckle on your finger) so that your wrists are aligned as well. This allows you to roll our wrists as you swing and get more torque on the bat. If this is uncomfortable, you should get them as close as possible. Remember that it is important to establish a routine so that you can establish muscle memory, giving you a smooth, strong stroke. When awaiting the pitch your body should already be in position to swing, elbow up and back to give a larger range of motion, which increases the force behind the bat. Don't change your form on delivery; any last second adjustments will change your angle to the ball, making it more likely for you to miss everything our foul off.
Third, squish the bug. The core muscles are another great source of power in hitting the ball. They channel the strength from your legs into the bat. These two muscles combined are much more powerful than your shoulders and arms could ever be. As you make your swing, snap your hips through and grind the bug with you back foot while you transfer your weight to your front foot and into the ball.
Fourth, is timing, you will never be a great hitter without it. This is where many players fail to achieve and it makes the difference between a foul ball, rolling grounder, or home run. The goal is to get the swing, step, and snap of the hips timed so that all the force goes into the bat at the most critical point, when it strikes the ball. The only way to develop timing is a great deal of practice. Using batting cages, hitting off a tee, soft toss, and even practicing the motion in your mind are great ways to get results. You have to put in the time in order to reap the benefits.
Learn how to hold a baseball bat properly and watch your swing and speed improve. Baseball is often thought of as sluggish and steady.